I've searched for answers here and at NASIOC (which appears to be down at the moment) on this issue. The short version is that I can't get any heat from my car with a fully warmed engine while at idle. Any other RPM level produces correspondingly hotter temps from the heater. My first guess is thermostat but the car has only 65K miles. Also, wouldn't the symptoms indicate the thermostat is staying open? When they fail don't they normally fail in the closed position. The car exhibits no overheating symptoms. Thanks for any help you can provide.